?...How about a circlotron using SJEPR100s and no source resistors?
Agree - that's what I have been working on recently on the recently neglected (by me) thread. Looks promising I think.
?...How about a circlotron using SJEPR100s and no source resistors?
Excellent work Ilquam.
I am jealous of your skills. Why do you think the cascade will allow for deletion of Rs. What affects does it have on stability of the outputs which would traditionally need help.
I am jealous of your skills. Why do you think the cascade will allow for deletion of Rs. What affects does it have on stability of the outputs which would traditionally need help.
I had read abut Rs and high order distortion. Mosfets with low Rs are hard to find, correct. Early effect i hpave heard, but mostly in bjt circles.Finally someone took the bait!
Source degeneration and cascoding are largely independent design choices, but in combination they help minimize output stage generated harmonics.
If you analyze the MOSFET equation for drain current vs. gate voltage, you find that two parameters contribute to 3rd order and higher harmonics: the internal and external source degeneration resistance Rs, and the Lambda parameter "Early Effect".
- Eliminating the external source resistors greatly reduces the higher order harmonics due to the local feedback in the output stage.
- Choose MOSFETs with low Rs.
- Cascoding eliminates the contribution due to the Early Effect.
I had read abut Rs and high order distortion. Mosfets with low Rs are hard to find, correct. Early effect i hpave heard, but mostly in bjt circles.
Somebody has to be the fish.
I would imagine a servo is in you future.
Still impressed. Pass has patent on cascode output. Have you looked at it?
Can you send me a pointer about that?Pass has patent on cascode output. Have you looked at it?
Pass has patent on cascode output. Have you looked at it?
Reducing early effect is like saying that you are working in constant voltage mode. Make scurrent only dependent on gate voltage.
oooo cool! what happens if you take a F6 say and cascode the outputs or maybe a stock f5 and cascode outputs ? impact on measured thd/sonics/spectra ? I think you mentioned somewhere above that you have done this already... Dunno much about this but sounds like something for nothing no ?
Do I?
Then a lot of people owe me some money!
Since you are biting your nails for the next episode:
Cascoding the output stage allows for very high output from only a single modulating FET on each rail without power dissipation problems. This also means that each driver stage is only driving the capacitance of a single FET.
Multiple cascode FETs are paralleled, with small source resistors to minimize current hogging. Most of the power is dissipated here.